31results about How to "Eliminate overvoltage" patented technology

The invention discloses an asymmetric operational control method of the direct current side monopolar grounding fault of an MMC-HVDC system. For the MMC-HVDC system based on monopolar symmetric wiring, after a direct current side monopolar grounding fault occurs, over voltage and fault current at AC and DC sides can be rapidly eliminated by setting the DC component of the output voltage of a bridge arm of a fault pole without locking a current converter, and further the insulation threat to AC / DC systems can be eliminated. Through adjusting phase angles of alternating components of different bridge arm voltages, the system still can continue transmitting half of a rated active power and provide reactive power support for the AC system while isolating the direct current side monopolar grounding fault, which has positive significance for the stability of the connected AC / DC systems; during the fault period, the current converter does not need to exit from operating, the restore speed of the system is high, the current converter is in a controlled state in the whole process, and therefore the active defense capability of the MMC-HVDC system based on monopolar symmetric wiring against the direct current side monopolar grounding fault can be improved.

A line selecting system for automatic tuning if arc quenching coil in 8421 parallel reactor integrated type and earthing fault of small current includes is prepared as forming said system by five reactors with one being used always as basic volume and the other four being used in rated value, connecting each of said four reactors to a vacuum high voltage contactor to form sixteen uniform volume of reactor, operating system on over - compensation mode with said four reactors on operation and operating system on full - compensation mode to ensure arc quenching by switching on or off reactor in optimum way when single phase earthing fault is existed on system.

An electronic ballast for at least one gas discharge lamp (LA), preferably for a fluorescent tube, having a rectifier circuit (2) connectable to a supply voltage source, a smoothing circuit (3) connected to the output of the rectifier circuit (2) for generating an intermediate circuit voltage (UZ), and an inverter (4), fed with the intermediate circuit voltage (UZ), to the output of which a terminal for the load circuit (5) containing the lamp (LA) is connected, and an overvoltage monitoring device which monitors the supply voltage (U0) delivered to the electronic ballast, whereby in the event that the supply voltage exceeds a predetermined nominal value (Ui,max), an optically or acoustically perceptible warning signal is issued.

The invention discloses a power supply soft input controlling method and the controlling device for a walking-beam pumping unit under intermittent power supplying. The method of the invention measures the rotation speed of an electromotor by detecting the residual voltage of a stator winding after blackout when the electromotor supplies power intermittently, can complete the soft input of the power supply within a short time using a silicon controlled rectifier switch component to exert voltage step by step when the real speed of the electromotor approaches the synchronous speed. The controlling device of the invention includes a man-machine interface, a detection unit, a main controller, and a switching component. The invention measures the rotation speed of the electromotor by detectingthe residual voltage of the stator winding after blackout, dispenses with a rotation speed sensor, and has high speed and precision. The silicon controlled rectifier component controls the on-off of the intermittent power supply, eliminates the overvoltage during the breakout due to the characteristic that the current is shut down when exceeding zero. Controlling the trigger of the silicon controlled rectifier around the synchronous speed when the electricity is turned on can implement the rapid soft input of the power supply, and then the impact current and the mechanical vibration can be avoided.

The invention relates to the technical field of access and control of power grid new energy, and designs an overvoltage protection system with high reliability and compact structure directing at the structure of a movable type photovoltaic power station low voltage ride-through testing apparatus and the operating characteristics of each main parts of the movable type photovoltaic power station low voltage ride-through testing apparatus so as to guarantee the operating safety of the power grid and the testing apparatus. The distributed overvoltage protection system includes a system inlet / outlet lightning protection system, an apparatus operation overvoltage protection system and a reactor overvoltage protection system, wherein the system inlet / outlet lightning protection system includes a system inlet lightning arrester set F1 and a system outlet lightning arrester set F2; the apparatus operation overvoltage protection system includes a current limiting reactance lightning arrester set F3 and a short circuit reactance lightning arrester set F4; and the reactor overvoltage protection system includes sectional type parallel lightning arrester sets F5-F6 which are arranged on each reactor in parallel connection in the movable type photovoltaic power station low voltage ride-through testing apparatus.

The invention discloses an AC load start-stop control circuit, which comprises a main circuit and a control circuit, wherein the main circuit comprises a voltage zero crossing point starting circuit and a current zero crossing point stopping circuit, a starting switch is cascaded in the voltage zero crossing point starting circuit, a stopping switch is cascaded in the current zero crossing point stopping circuit, a normally open contact of a relay in the voltage zero crossing point starting circuit and a normally closed contact of a relay in the current zero crossing point stopping circuit are connected to the control circuit. By using chances of AC voltage and current periodic zero crossing points, the voltage zero crossing point starting control and the current zero crossing point stopping control of an AC load circuit are realized, overvoltage and overcurrnet generated from starting and stopping instantly are eliminated, and impaction caused to a power grid can be relieved to ensure that the whole power grid is greatly reduced. The AC load start-stop control circuit has the advantages of stable work and high reliability.

The invention relates to a device (2) for limiting an overvoltage in the DC link (18) of a traction power converter. The inventive device (2) comprises two interruptible semiconductor switches (T7, T8) that are electrically connected in series, an inductor (48), a double-layer capacitor (50), and a resistor (54) which can be connected by means of a switch (S1). The inductor (48) and the double-layer capacitor (50) are electrically connected in series while said series connection is connected between an interconnection point (46) of the two interruptible semiconductor switches (T7, T8) and a negative conductor rail (20) of the DC link (18). Additionally, the connectable resistor (54) can be electrically connected parallel to the double-layer capacitor (50), resulting in a device which is structured in a particularly simple manner and by means of which overvoltages occurring in the DC link (18) of a traction power converter can be suppressed.